Field of the Invention
The present invention relates generally to electric motors and, more particularly, to a reduced weight rotor for use in such motors.
Description of the Prior Art
Electric motors have been in existence for over one hundred years now. Despite this, today there is a renewed interest in them due to an ever-increasing concern about the environmental impact of other forms of power generation such as gasoline engines.
One known form of electric motors is commonly referred to as a brushless permanent magnet motor due to its design and operation. Referring now to FIG. 1, a simplified diagram of just such an electric motor can be seen. As shown in the figure, motor 100 comprises a stationary part referred to as a stator 102 and a rotating part referred to as a rotor 104. In this example, stator 102 includes three separate phase wire windings, labeled phase A wire winding 106, phase B wire winding 108, and phase C wire winding 110 in the figure, each of which includes wire wound around an armature, known as a tooth, of stator 102. As is known in the art, the space along the stator between two neighboring teeth is commonly referred to as a slot. As also shown in this example, rotor 104 includes two permanent magnet poles labeled magnet N 112 (for North) and magnet S 114 (for South), about its periphery. This stator and rotor electric motor configuration is known as an “inrunner” because the rotor is located inside the stator (versus an “outrunner” where the physical relationship between the stator and rotor is reversed) and, in either configuration, the physical space or gap between the teeth of stator 102 and the permanent magnets of rotor 104 is commonly referred to as an air gap.
In operation, a motor controller (not shown) provides electric current across the three winding phases (e.g., phase A wire winding 106, phase B wire winding 108, and phase C wire winding 110) in a sequential fashion around stator 102 thus making it a three-phase motor. As current is running through a given wire winding it generates a local magnetic field which then repels and/or attracts any nearby permanent magnets such as permanent magnet N 112 and permanent magnet S 114 of rotor 104 thereby causing rotor 104 to spin or rotate about its axis. In this way, electric motor 100 can be applied to a variety of uses by, for example, having a drive gear (not shown) located on a spinning shaft 116 at the axis of rotor 104.
In further explanation and by way of example, the motor controller (not shown) applies a positive voltage to one end of the phase A wire winding 106 and a negative voltage to one end of the phase B wire winding 108. This voltage differential creates an electric current from the one end of the phase A wire winding 106 to a “Wye” termination and then to the one end of the phase B wire winding 108 because, as shown in the figure, the other ends of the phase A wire winding 106 and the phase B wire winding 108 (as well as that of one of the ends of the phase C wire winding 110) are electrically connected in the form of a “Wye” termination, a form of termination connection known in the art. This electric current, as explained above, creates a magnetic field surrounding the wire windings, such as phase A wire winding 106 and phase B wire winding 108. These magnetic fields repel (and/or attract, as the case may be) respective ones of magnet N 112 and/or magnet S 114 thereby causing rotor 104 to spin about it axis. The motor controller then applies a voltage differential across one end of the phase B wire winding 108 and one end of the phase C wire winding 110 causing rotor 104 to continue to spin. The motor controller then applies a voltage differential across one end of the phase C wire winding 110 and one end of the phase A wire winding 106 causing rotor 104 to further continue to spin. This process is repeated thus continuing to cause rotor 104 to spin or rotate within stator 102.
It is to be understood that the diagram of motor 100 of FIG. 1 is a simplified form of such an electric motor. As is known in the art, increasing the size and number of the active motive elements, such as the size of the stator and the number of windings (as well as the number of wire windings on each tooth) on the stator and the size of the rotor and the number (and power) of magnets on the rotor, increases the motive force or power of the electric motor. Therefore, in practice, it is common for each of the phase wire windings to be duplicated (so that there is more than one phase A wire winding 106, more than one phase B wire winding 108, and more than one phase C wire winding 110) at additional teeth locations around a stator thereby providing additional magnetic fields to repel (and/or attract) any magnets on a rotor. Likewise, it is common for each of the magnets of a rotor to be duplicated (so that there is more than one N magnet 112 and more than one S magnet 114) thereby providing additional magnets to be repelled (and/or attracted) by a stator's wire windings.
Referring now to FIG. 2, an exploded diagram of an electric motor 200 of the prior art can be seen. As shown, electric motor 200 includes a drive end plate 202, a motor casing 204 having radial heat fins for passive air cooling, a stator 206 comprising a set of stacked laminations and wire windings (not shown), a rotor 208 comprising permanent magnets located about its periphery, and a rear end plate 210.
It is to be understood that the basic physical relationship and operation of these elements in motor 200 is generally as was described with respect to that of motor 100 of FIG. 1. In particular, rotor 208 fits within stator 206, separated by an air gap, both of which then fit within motor casing 204 with drive end plate 202 attached to and closing a front end of motor casing 204 while rear end plate 210 is attached to and closes a rear end of motor casing 204. As has been explained, rotor 208 is then caused to rotate within stator 206, by the application of a voltage differential across the wire windings on stator 206 which repel and/or attract the magnets of rotor 208.
Of course, a given motor may be limited in how physically large it can be for a given use case thus limiting the extent of any increases in active motive material (e.g., the size of the stator, the number of wire windings and/or number of wire windings per tooth, the size of the rotor, and the number and power of the magnets). Further, within any overall size constraints for a given motor, it may be desirable to reduce the motor's weight in order to improve its performance characteristics and/or overall usefulness for a given application.